Solid state lighting such as LED lighting is rapidly gaining popularity due to the green credentials of such lighting. Typically, solid state lighting devices produce their luminous outputs at a fraction of the energy consumption of incandescent or halogen lighting devices. In addition, solid state lighting devices have superior lifetimes compared to incandescent and halogen lighting devices.
In order to generate a luminous output of sufficient intensity, a solid state lighting device typically comprises a plurality of solid state lighting elements, which may be arranged in a regular pattern in other to obtain a homogeneous luminous output. For example, the solid state lighting device may be provided as strip lighting in which a plurality of solid state lighting elements, e.g. LEDs, are mounted on an elongate, e.g. a rectangular, strip such as a flexible carrier strip. Such flexible strips are sometimes referred to as flexible printed circuit boards.
An example of such a lighting device is schematically depicted in FIG. 1, which depicts a tubular solid state lighting device 10 in which a portion of the major surface 22 of the flexible carrier strip 20 is attached to an inner wall section of the tube 12 that axially extends along the tube 12, i.e. the flexible carrier strip 20 is secured along a length direction of the tube 12. This is typically achieved using an adhesive such as glue or a double-sided tape. The flexible carrier strip 20 further comprises a major surface 21 having a region in which solid state lighting elements 30 are arranged to emit light into the tube 12. The tubular solid state lighting device 10 further comprises a rigid printed circuit board (PCB) 40, which may be mounted in an end cap 11 of the tubular solid state lighting device 10 and which typically has a driver circuit 50 mounted on a major surface 42 facing the major surface 21 of the flexible carrier strip. The flexible carrier strip 20 typically comprises an end portion 24 having one or more solder contacts on the major surface 21, which are soldered to corresponding solder contacts on the major surface 42 of the PCB 40.
A typical assembly process of such a tubular solid state lighting device 10 involves the securing of the flexible carrier strip 20 inside the tube 12 such that part of the flexible carrier strip 20 including the end portion 24 sticks out of the tube 12. The rigid PCB 40 is subsequently soldered to the flexible carrier strip 20 after which the rigid PCB 40 is inserted into the tube 12 as indicated by the block arrow, e.g. by capping the tube 12 with the end cap 11. During this process, an intermediate portion 23 of the flexible carrier strip 20 is pushed inwardly to form a meandering region between the first portion of the flexible carrier strip 20 onto which the solid state lighting elements 30 are mounted and the end portion 24 such that the flexible carrier strip 20 folds back on itself.
However, this assembly process suffers from a high failure rate. Specifically, the solder joints between the flexible carrier strip 20 and the rigid PCB 40 are prone to failure due to the fact that the insertion of the rigid PCB 40 into the tube 12 causes these solder joints to be subjected to sheer or peel-off stress associated with pushing the intermediate portion 23 of the flexible carrier strip into the tube 12. Such a failure rate may be reduced by reinforcing the solder joints, e.g. using a double-sided adhesive tape or glue, by more prolonged soldering using additional solder or by inspection of the solder joint, e.g. using x-ray inspection.
U.S. Pat. No. 5,920,465 discloses a connecting structure for interconnection of a flexible printed circuit board (FPC) and a hard printed circuit board (PCB) allowing the FPC and the PCB to be easily connected to each other at a predetermined relative position by fitting a male joint of the FPC into a female joint of the PCB even when a supporting member, such as a casing, is not available immediately below portions of the PCB and FPC to be connected to each other. In the connecting structure for interconnection of an FPC and a PCB, a surface of the FPC opposed to the PCB is provided with a male joint in the form of a protruding plate, and a surface of the PCB opposed to the FPC is provided with a female joint in the form of an opening or a recess adapted to receive the protruding plate and thereby to position the FPC at a predetermined location of the PCB.
These measures all have in common that the improved robustness of the connection between the flexible carrier strip and the rigid PCB increase the complexity and/or manufacturing cost of the tubular solid state lighting device 10. This is undesirable, for example because the additional cost of solid state lighting devices compared to traditional incandescent, halogen or fluorescent lighting devices is one of the main obstacles on the road to large-scale replacement of such traditional lighting devices with the more energy-efficient solid state lighting equivalents.